Nov. 12, 1917 Greenhouse Fumigation with Hydrocyanic Acid 
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EFFECT OF THE ENZYMIC ACTIVITIES OF THE PLANTS 
Geppert’s (10) work has proved conclusively that in the higher 
animals absorbed hydrocyanic acid limits oxygen transfer in the tis¬ 
sues. Loevenhart and Kastle (12) have shown that the gas is able 
to paralyze the catalytic activity of solutions of metallic colloids. 
Kastle and Loevenhart (u) showed that hydrogen cyanid inhibits the 
action of potato oxidases, while recently Shafer (19) has shown that it 
affects the activities of oxidases, catalase, and reductase in insect tis¬ 
sues. One would expect, therefore, to find that in plants which had 
absorbed hydrocyanic acid during fumigation the respiratory enzyms 
at least were affected. Enzyms other than those connected with res¬ 
piration were tested for the effect of hydrocyanic acid as follows: Com¬ 
mercial pepsin acting on coagulated white of egg; proteases extracted 
from tomato leaves acting on coagulated fibrin; taka diastase and dia¬ 
stase from tomato leaves acting on soluble starch; zymase acting on 
dextrose; rennin. The result in each case was that there was no appar¬ 
ent effect on these enzyms, either in speed of action or in total change 
produced. 
Among the respiratory enzyms studied were oxidases, catalase, and 
reductase. In this paper these terms should be construed as follows: 
Oxidases are the substances which will cause transfer of atmospheric 
oxygen to aromatic chromogens, such as hydroquinone, pyrogallol, and 
the cresols. Catalase liberates molecular oxygen from hydrogen per- 
oxid. The reductase activity sought here was the decolorizing of 
methylene blue in the absence of oxygen. Two kinds of preparations 
for enzym work were used: First, the juice of the leaves, obtained by 
grinding them in a food chopper and squeezing through silk bolting 
cloth; second, the dried leaf powder, obtained by drying the leaves in 
a vacuum desiccator over quicklime, then powdering in a mortar and 
sifting through No. 12 bolting cloth. 
Oxidases. —For the quantitative determination of oxidase activity 
Bunzel’s (6) simpler apparatus was employed. A temperature of 37 0 C. 
was used in all determinations; 0.1 gm. of leaf powder was allowed to 
act on 0.01 gm. of oxidizable chemical until the reading was constant, 
usually 1.5 to 2.0 hours. As a preliminary a number of oxidizable 
chemicals were tried. Since pyrocatechol and hydroquinone gave the 
best results, they were used in this work. 
In order to demonstrate that the presence of hydrocyanic acid inhibits 
oxidase activity, powder from normal tomato leaves was placed in one 
arm of the Bunzel tubes and varying concentrations of hydrogen cyanid, 
together with hydroquinone, were placed in the other arm. In this way 
the cyanid and the leaf powder did not come in contact except during 
the reaction period. The results are shown in figure 1. It is evident 
that there is a rapid decline in activity in the presence of even very 
small amounts of the poison. 
